Preparation of aminoazobenzenes



Patented Jan. 16, 1951 PREPARATION GE" AMINOAZOBENZENES George Shulman, West New York, N. J assi'grior to Pfister Chemical Works- 1310;, Riiilgefield, s N; 1., a corporation of NewJerscy- N0. Drawing,

. f This invention relates to improvements-in. the. processof. manufacturing. aminoazobenzene' and. its derivativesandsalts thereof.

3 Thegeneral. formula for the. products which maybe made by the processol the inventionis Where as stands-for 'H'ora-nalkyl-or alkoxy group.

Heretoforethese compounds-havebeen made by a one stage processor a multistage process'. In the one stage process, for example, sodium nitriteis add'ed slowly to asolution of aniline in half its equivalent of'hydrochloric aci'd Diazot'ization, couplin and iscm'erizat'ion all take-place inthe onereaction mixture. This process is seldom'used'; however, because extremely" powerful agitators are" required" to stir'theviscous' reaction mixture and good.

The multistage process, which givesa much purer product, is lengthy and requires considerable equipment. It may; for-example, be conducted. as follows:- First, aniline is diazotized in solution in hydrochlori'c'acid with an equivalent amount of sodium nitrite: Secondlflan acid sol-ution of anilineis added" to the diazoniurn' com pound produced by the first step and-slowly coupled by" theadd Ion of alkali such as amm'on-ia.- The resultant 'di'azoi-minob'enzene is iso lated' by filtration and then isomeriz'ed-ina third step byhe'atin-g a large excess ofaniline. The process of the invention is a modification: of the one stage process, which overcomes it's--disadvantages, the" new process being characterized by the use of a monohydric alcohol containing not over three carbon. atoms as a medium in which: the: intormediatev diazoimino. compound produced by diazotization isisomerized theaminoa-zo compound the process being carried out under certain essential time and temperature conditions, as hereinafter exp'l'ained. I

F The alcohols which may be. usedas the medium in which theisomerizationis carried out are methanol, ethanol, n-propanol and isopropanol.

Aniline the puritypof the product is not ApplicatiolrJanuary 6-; v Serial No. 69,630 V 1' Claim. (01. 260 -205) before isomerization ii the diazoimino. compound is: alcoholic" solution. However, it) has. been. discovered that if the-process is. carried" out. are period. not. exceeding, minutes from the. com mencement' of the additionv off. the diazoti'zation agent within.temperaturelimits between 10 and 40 (31., isomerizationis successfully: effected; with; out decomposition and a product closely comparable in purity with that produced by themulti stage ,process is obtained.

The starting material may be anilineor 'alkyl derivativesthereof-such as" o-tol'uidine (methyt anilin'ei or al'koxy derivatives-suchas o-anisidine Qmethoxy aniline-l and? o-phcnetidine ('ethoxy aniline), depending on: the product desiredi Diazotization of thestarting' material is or: f'ected by 'usua-l agent's; preferably sodium nitrite, othe'riagents capable ofuse being potassium{ni trite, nitrous acid, organic nitrites such as'ramyl of'conversiorr to nitrous acid in water.' I I In practicing the invention the starting" Ina;- teri'al, aniline or. a-derivative' thereof, mixed with one of the above-mentioned lower aliphatic monohydric alcohols andihydro'chloric acids This admixture, which. becomes heated on mixing, then cooled to about. 25? to30 CJ. and. the sodium nitrite or other diazotizing agent is slowly added with cooling so as to Keep the temperature below 4 09,, and preferably between 20 and 30, while the mixture is. stirred; Diazotization,.. coupling and isomerization all take place in the one reac. tion mixture the starting material being comvertecl. to a diaz0nium-. salt which couples with excessc-startingamaterial forming.- a diazoinnno: compound. which: turn. isomerizes to form the: basic aminoazm compound; The: base maybe res coreredi as a precipitate by dilution. of the IIliX+- ture' witlri'a .laxg lquantity of "Water or by: addi, ti'orrofalkali. such as: sodium hydroxide, or may beconverted to ai'salt, as by addition of hydro chloric' acid and recovered 'as such. Removal of: the fin [product may be-efiected by'filtration; wash rig nd dryingand further purificatibn effect y vacuum. distillation; V The reactions which; occur informing ,the'base or ethyl nit-rites; and gaseous products-capable maybe indicatedras" follows."

Benzenediazonium Diezoiminobenzene p-Aminoazobenzeno Success of the process, wherein isomerization of the diazoimino to the aminoazo compound takes place in the aicohol medium, depends upon completing it rapidly and upon cooling the mixture the reaction, which is exothermic, and in Fusing the proper proportion of alcohol. Atfno'jtime should the temperature be outside the range to 40 C. and the preferred range is 20 to 309. The time should not be more than 45 minutes at 20 to 30 and preferably'the reaction time should be from to 30 minutes. On a laboratory scale it is possibleto cool the mixture adequately by immersing the reactio vessel in an ice water bath. On a plant scale, however, this 1 isyiinpossible because no external cooling means can -be adequate to meetthe requirements, The internal method of cooling-normally used, namely the addition of ice,,ca nnot be employed because it would completely inhibit isomerization. This cooling problem is met by the addition of solid carbon'dioxide simultaneously with the sodium nitrite or other diazotizing agent and this cools the mixture without detrimental side effects. 1 Illustrative of how the invention may be carried out in practice are the following specific ex amples,Example 1 being a laboratory scale preparation and Example 2 being a plant scale operation. 1 V H Example 1 Mix 42.8 gr. ortho toluidine, 27 gr. isopropyl alcohol (63% by weight, based .on the weight of the ortho toluidine) and ,2? gr. hydrochloric acid Be). The temperaturerises to 50-60 C. Cool to C. and slowly sprinkle in 14 gr. sodium nitrite over a period of ;minutes while stirring and cooling the reaction mixture in .a bath'of ice water to maintain the temperature between 20 and 30 C. A reddish-brown viscous oil phase forms'on'top of a water phase containing dissolved sodium chloride. After all of the sodium nitrite has been added, stirring is continued for fiveminutes and then 27 gnhydrochloric acid (20 B.) is added tojconvert the aminoazotoluene base to the hydrochloride. The product is then filtered and the filtrate washed with dilute h'ydrochloricjacid anddried. The yield is practically quantitative, 50 to 52 gr.

k Example 2 between 30 and CZ An oily product results, as inExample 1, and this is drowned in 500 lbs.

/ of 15% hydrochloric acid. Para aminoazobenzene hydrochloride separates in the form of very fine particleswhich are isolated from the liquidby filtration, washed with dilute hydrochloric acid At the same time, solid" carbon dioxide is added to the reaction mixture at such a rate as to".keep the-temperature thereof 4 comparable to that produced by the more complex and time-consuming multistage process described above.

Final purification of the product may be effected by vacuum distillation.

From the foregoing examples it will be noted that the proportion of alcohol, 63% and 71% in the examples, respectively, is very much less than would normally be used for solvent purposes. This restriction in the amount of alcohol is essential to the success of the process. 'If a relatively large quantity of alcohol, such as is usually used for solvent purposes, is present, no isomerization will take place both in a short time and at low temperatures. Some isomerization may take place after several days at low temperature but large amounts of tar will also be formed due to decomposition. Some isomerization would take 5 and dried at 50 to C. The yield is 450 to 460 6 pounds and the purity of this product is closely place in a short time if the solution were heated but large amounts of tar would likewise be formed. In other words, the optimum conditions for the process (low temperature and short time) cannot be realized :with the use of alcohol unless the proportion of alcohol is restricted as indicated by the examples. The total amount of alcohol by weight, based on the weight of the aniline or aniline derivative, is preferably in the range 50% to The invention thus provides a much simpler and more economical process of producing aminoazobenzene compounds of a desirable degree of purity which may be carried out with a minimum of equipment. The said compounds, produced by the process of the invention, have well known uses in the dye industry.

It is to be understood that the specific examples are to be construed as merely illustrative of the invention and not as limitations thereon, various modifications in the process being contemplated as falling within the invention as defined in the claim.

What is claimed is:

. The process of making aminoazotoluene which comprises admixing a diazotizing agent with a solution of ortho toluidine in hydrochloric acid and a monohydric aliphatic alcohol containing not more than three carbon atoms in which the quantity of alcohol is in the proportion, by weight, to the ortho toluidine of from 63% to 71%, during a period of from 15 to 45 minutes, while maintaining the temperature of the reaction mixture between 10 and 40 C., and immediately separating the amirioazotoluene from said mixture.

GEORGE SHULMAN.

REFERENCES CITED --The following references are of record in the fileof this patent} I UNITED STATES PATENTS Number Name Date 2,007,510 Thornton July 9, 1935 

